Cathode ray tube



May 16, 1944. K. SCHLESING ER CATHODE RAY TUBE Filed NOV. 5, 1938 v Inventor:

lfurhS h/es/nger 6} L4- Af/orney scanning a substantially Patented May 16, 1944 Kurt Schlesinger, Berlin Germany: vested in the Alien Property Custodian Application November 5, 1938, Serial In Germany May 31, 1938 2 Claims.

In Braun tubes with mixed electrostatic and electromagnetic deflection there is found on the fluorescent screen after a period of operation of several hours a dark line which extends transversely through the image field parallel to the magnetic and electric lines of force.

The line results from the impact of ions on the fluorescent screen. As well known the deflection in electrostatic flelds is independent of the mass of the particles, whereas an electromagnetic field causes a splitting of the bundle of rays owing to the diflerent effect of particles of different mass. If, for example, in the case of a televisiontube, the screen is scanned by combined electrostatic and electro-magnetie deflecting means, the conditions are such that the ions in the'electrostatic field are deflected in exactly the same fashion as the electrons, wherev as in the magnetic field they are hardly-appreciably aii'ected. The ions accordingly pass over a fairly sharp line through the centre of the image field parallel to the magnetic and electric lines of the field.

The ions meet against the fluorescent screen with great kinetic energy. Since at the present time sulphide is the chief material employed for the screen, the black line results under the well known greatly reducing action of the ions by reduction of the zinc sulphide, and-consists of a thin layer of metallic zinc.

It is an object of the present invention to provide means for avoiding the just described disturbing influence of the negative ions in a cathode ray tube which is operated with means including at least one pair of magnet coils for rectangular area of the screen.

According to the invention there is provided in the space between the anode and the lust mentioned scanning means an additional pair of defleeting plates, the lines of force of which, in operation, are substantially perpendicular to the lines of force of the magnet coils forming part of the scanning system. These deflecting plates are supplied with a constant potential of such nature that the ray, in its position of rest, is deflected beyond the extreme edge of the image. Since this preliminary deflection takes place el ostatically the electrons and the ions are acted upon in equal fashion. v

By means of a direct current traversing the deflecting coils referred to. the ray is again deiiected back to the center of the image fleld. 'Since this deflection occurs magnetically. it is only'the electrons which respond' to the same, 86

whilst the interfering ions leave the image screen in the direction determined by the preliminary electrostatic deflection.

The varying deflection of the image point for scanning the screen takes place asbefore by the usual methods.

The invention will be better understood with the aid of and further features-of the invention will be apparent from the following more detailed description and the accompanying draw ing of which in a purely diagrammatic fashion and by way of example 1 Fig. 1 shows the tube according to the invention in an axial section parallel to the planes of the main deflecting plates, and some essential circuit elements,

Fig. 2 is a sectional view, vertical to that of Fig. 1, of the deflecting space,

Figs. 3 and 4 illustrate certain modifications of the connection of -a tube according to Fig. 1.

In the drawing, I is the anode, 2 and time the main deflecting plates for the electrostatic deflection in the direction of they lines of the image, 4 and 5 are the coils for the magnetiedeflection vertical to the direction of the lines, and 6 and I are two sheet iron boxes, which in the known fashion act as pole shoes for the electromagnet. v

According to the invention, there are located in the space between the anode l and thedefleeting means 2 and 3 or 4 and 5 an additional pair of deflecting plates, which consist of two plates 8 ands of non-magnetic sheet metal. The deflecting plates) and 9 are applied with the aid of two potential sources is and ii to potentials which are preferably symmetrical with relation to the anode potential, and which are so selected that electrons and ions are deflected in common by at least one-half of thewidth of the image fleld, the ray n its stationary condition accordingly impinging on the image screen I! at the point P. In order now again to return the electrons alone to the centre point Q of the image screen an auxiliary direct current, which is supplied by a current source i3 indicated diagrammatically in Fig. 1, is passed through the deflecting coils 4 and- 5. electronic ray alone is deilec'tedback to the centre of the image.

passes to Q, whilst the ionic ray passes to the point P situated outside of the image fleld.

The requisite auxiliary potentials can be derived from the existing mains apparatus. It is also possible to dispense with one of these potentiais by connecting the plate 8 in direct In this manner the' The electronic ray accordingly.

of the boxes against anode and said deflecting system,

same the interfering eflect of the ions makes itself noticeable by the occurrence of a black spot at the centre of the image field.

1. In a discharge tube arrangement in combin'ation a cathode ray tube comprising a luminescent screen and means including a cathode and an anode for producing a cathode ray and for focusing said cathode ray on said screen, a deflecting system arranged between said anode and said screen and comprising a pair of magnet coils, for causing said ray to scan said screen, a pair of deflecting plates mounted between said said pair of deflecting plates being so arranged that, in operation, the lines of force of said deflecting plates extend substantially vertically to the lines of force of said coils, means for connecting the one plate of said pair inside said tube to said anode and means for providing the other plate of said pair with such a potential with respect to said anode that said cathode ray in its stationary position is deflected out of the image field.

2. In a discharge tube arrangement in com bination a cathode ray tube comprising a luminescent screen and means for focusing said cathode my on said screen, a

' deflecting system arranged between said anode and said screen and comprising a pair of magfor causing said ray to scan said screen. a pair of deflecting plates mounted between said anode and said deflecting system, said pair of deflecting plates being so arranged that, in operation, the lines of force of said deflecting plates extend substantially vertically to the lines of force of said coils, means for connecting the one plate of said pair inside said tube to said anode, and means for connecting the other plate of said pair inside said tube to an electrode of said tube other than said anode, said other electrode bein connected to a source of potential of such an amount with respect to said anode that said cathode ray in its stationary position is deflected out of the image field.

KURT SCHLESINGER.

including a cathode and an anode for producing a cathode ray and 

